Request For Comments - RFC7279

Internet Engineering Task Force (IETF) M. Shore
Request for Comments: 7279 No Mountain Software
BCP: 189 C. Pignataro
Category: Best Current Practice Cisco Systems, Inc.
ISSN: 2070-1721 May 2014
An Acceptable Use Policy for New ICMP Types and Codes
Abstract
In this document we provide a basic description of ICMP's role in the
IP stack and some guidelines for future use.
This document is motivated by concerns about lack of clarity
concerning when to add new Internet Control Message Protocol (ICMP)
types and/or codes. These concerns have highlighted a need to
describe policies for when adding new features to ICMP is desirable
and when it is not.
Status of This Memo
This memo documents an Internet Best Current Practice.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
BCPs is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7279.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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RFC 7279ICMPAUP May 2014
In summary, any future message types added to ICMP should be limited
to two broad categories:
1. to inform a datagram's originator that a forwarding plane anomaly
has been encountered downstream. The datagram originator must be
able to determine whether or not the datagram was discarded by
examining the ICMP message.
2. to discover and convey dynamic information about a node (other
than information usually carried in routing protocols), to
discover and convey network-specific parameters, and to discover
on-link routers and hosts.
Normally, ICMP SHOULD NOT be used to implement a general-purpose
routing or network management protocol. However, ICMP does have a
role to play in conveying dynamic information about a network, which
would belong in category 2 above.
2.1. Classification of Existing Message Types
This section provides a rough breakdown of existing message types
according to the taxonomy described in Section 2 at the time of
publication.
IPv4 forwarding plane anomaly reporting:
3: Destination Unreachable
4: Source Quench (Deprecated)
6: Alternate Host Address (Deprecated)
11: Time Exceeded
12: Parameter Problem
31: Datagram Conversion Error (Deprecated)
IPv4 router or host discovery:
0: Echo Reply
5: Redirect
8: Echo
9: Router Advertisement
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RFC 7279ICMPAUP May 2014
147: Mobile Prefix Advertisement
148: Certification Path Solicitation Message
149: Certification Path Advertisement Message
150: ICMP messages utilized by experimental mobility protocols
such as Seamoby
151: Multicast Router Advertisement
152: Multicast Router Solicitation
153: Multicast Router Termination
154: FMIPv6 Messages
155: RPL Control Message
2.1.1.ICMP Use as a Routing Protocol
As mentioned in Section 2, using ICMP as a general-purpose routing or
network management protocol is not advisable and SHOULD NOT be used
that way.
ICMP has a role in the Internet as an integral part of the IP layer;
it is not as a routing protocol or as a transport protocol for other
layers including routing information. From a more pragmatic
perspective, some of the key characteristics of ICMP make it a less-
than-ideal choice for a routing protocol. These key characteristics
include that ICMP is frequently filtered, is not authenticated, and
is easily spoofed. In addition, specialist hardware processing of
ICMP would disrupt the deployment of an ICMP-based routing or
management protocol.
2.1.2. A Few Notes on RPL
RPL, the IPv6 routing protocol for low-power and lossy networks (see
[RFC6550]) uses ICMP as a transport. In this regard, it is an
exception among the ICMP message types. Note that, although RPL is
an IP routing protocol, it is not deployed on the general Internet;
it is limited to specific, contained networks.
This should be considered anomalous and is not a model for future
ICMP message types. That is, ICMP is not intended as a transport for
other protocols and SHOULD NOT be used in that way in future
specifications. In particular, while it is adequate to use ICMP as a
discovery protocol, it does not extend to full routing capabilities.
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2.2. Applications Using ICMP
Some applications make use of ICMP error notifications, or even
deliberately create anomalous conditions in order to elicit ICMP
messages. These ICMP messages are then used to generate feedback to
the higher layer. Some of these applications include some of the
most widespread examples, such as PING, TRACEROUTE, and Path MTU
Discovery (PMTUD). These uses are considered acceptable because they
use existing ICMP message types and do not change ICMP functionality.
2.3. Extending ICMPICMP multi-part messages are specified in [RFC4884] by defining an
extension mechanism for selected ICMP messages. This mechanism
addresses a fundamental problem in ICMP extensibility. An ICMP
multi-part message carries all of the information that ICMP messages
carried previously, as well as additional information that
applications may require.
Some currently defined ICMP extensions include ICMP extensions for
Multiprotocol Label Switching [RFC4950] and ICMP extensions for
interface and next-hop identification [RFC5837].
Extensions to ICMP SHOULD follow the requirements provided in
[RFC4884].
2.4. ICMPv4 vs. ICMPv6
Because ICMPv6 is used for IPv6 Neighbor Discovery, deployed IPv6
routers, IPv6-capable security gateways, and IPv6-capable firewalls
normally support administrator configuration of how specific ICMPv6
message types are handled. By contrast, deployed IPv4 routers,
IPv4-capable security gateways, and IPv4-capable firewalls are less
likely to allow an administrator to configure how specific ICMPv4
message types are handled. So, at present, ICMPv6 messages usually
have a higher probability of travelling end-to-end than ICMPv4
messages.
3. ICMP's Role in the InternetICMP was originally intended to be a mechanism for gateways or
destination hosts to report error conditions back to source hosts in
ICMPv4 [RFC0792]; ICMPv6 [RFC4443] is modeled after it. ICMP is also
used to perform IP-layer functions, such as diagnostics (e.g., PING).
ICMP is defined to be an integral part of IP and must be implemented
by every IP module. This is true for ICMPv4 as an integral part of
IPv4 (see the Introduction of [RFC0792]), and for ICMPv6 as an
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RFC 7279ICMPAUP May 2014
integral part of IPv6 (see Section 2 of [RFC4443]). When first
defined, ICMP messages were thought of as IP messages that didn't
carry any higher-layer data. It could be conjectured that the term
"control" was used because ICMP messages were not "data" messages.
The word "control" in the protocol name did not describe ICMP's
function (i.e., it did not "control" the Internet); rather, it was
used to communicate about the control functions in the Internet. For
example, even though ICMP included a redirect message type that
affects routing behavior in the context of a LAN segment, it was not
and is not used as a generic routing protocol.
4. Security Considerations
This document describes a high-level policy for adding ICMP types and
codes. While special attention must be paid to the security
implications of any particular new ICMP type or code, this
recommendation presents no new security considerations.
From a security perspective, ICMP plays a part in the Photuris
protocol [RFC2521]. But more generally, ICMP is not a secure
protocol and does not include features to be used to discover network
security parameters or to report on network security anomalies in the
forwarding plane.
Additionally, new ICMP functionality (e.g., ICMP extensions, or new
ICMP types or codes) needs to consider potential ways that ICMP can
be abused (e.g., Smurf IP DoS [CA-1998-01]).
5. Acknowledgments
This document was originally proposed by, and received substantial
review and suggestions from, Ron Bonica. Discussions with Pascal
Thubert helped clarify the history of RPL's use of ICMP. We are very
grateful for the review, feedback, and comments from Ran Atkinson,
Tim Chown, Joe Clarke, Adrian Farrel, Ray Hunter, Hilarie Orman, Eric
Rosen, JINMEI Tatuya, and Wen Zhang, which resulted in a much
improved document.
6. References
6.1. Normative references
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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